Self-cleaning apparatus and method for thick slurry pressure control

ABSTRACT

Self-cleaning apparatus and methods are disclosed for handling viscous fluids, such as thick solid-liquid slurries of lignocellulosic biomass and its components, under high pressure, using an array of retractable valves.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Application No. 61/482,449,filed May 4, 2011, the entire disclosure of which is incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention generally relates to apparatus and methods forhandling viscous fluids. More particularly, it relates to self-cleaningapparatus and methods for handling viscous fluids, such as thickslurries of lignocellulosic biomass and its components, under highpressure.

BACKGROUND OF THE INVENTION

Backpressure control is critical to maintaining process conditions.However, with solid-liquid slurries, clogging of valves and orifices isa challenge. In addition, back pressure control valves cannot respondquickly enough and completely reseal to avoid bleed-through. Processpressure variations must be minimized to maintain process control. Thus,it would be beneficial to develop an efficient and reliable means forhandling fouling fluids, such as thick solid-liquid slurries oflignocellulosic biomass and its components, under high pressure thatminimize clogging, including, but not limited to those processed withcompressible supercritical or near-critical fluids. The apparatus ofmethods of the present invention are directed toward these, as well asother, important ends.

SUMMARY OF THE INVENTION

In one embodiment, the invention is directed to self-cleaning apparatusfor processing of a fouling fluid under pressure, comprising:

-   -   a passageway having at least two stages;    -   a retractable valve positioned in each of said at least two        stages; and    -   an optional shutoff valve positioned in said passageway;    -   wherein said retractable valves form a tortuous path in said        passageway when said retractable valves are partially closed to        permit a pressure drop between said stages; and    -   wherein at least one of said retractable valves is capable of        being in an open position when the other of said retractable        valves are partially closed.

In another embodiment, the invention is directed to methods for reducingfouling in processing of lignocellulolosic biomass, comprising:

-   -   providing a fouling fluid under pressure in an apparatus        comprising:        -   a passageway having at least two stages;        -   a retractable valve positioned in each of said at least two            stages; and        -   an optional shutoff valve positioned in said passageway;        -   wherein said retractable valves form a tortuous path in said            passageway when said retractable valves are partially closed            to permit a pressure drop between said stages; and    -   retracting at least one of said retractable valves to an open        position to form an open retractable valve when the other of        said retractable valves are partially closed to clean said open        retractable valve and to control pressure in said apparatus.

In yet another embodiment, the invention is directed to methods forcontrolling backpressure in processing of lignocellulolosic biomass,comprising:

-   -   providing a fouling fluid under pressure in an apparatus        comprising:        -   a passageway having at least two stages;        -   a retractable valve positioned in each of said at least two            stages; and        -   an optional shutoff valve positioned in said passageway;        -   wherein said retractable valves form a tortuous path in said            passageway when said retractable valves are partially closed            to permit a pressure drop between said stages; and    -   retracting at least one of said retractable valves to an open        position to form an open retractable valve when the other of        said retractable valves are partially closed to clean said open        retractable valve and to control pressure in said apparatus.

In further embodiments, the invention is directed to systems forprocessing fouling fluids, comprising:

-   -   at least one self-cleaning apparatus described herein; and    -   tortuous path piping;    -   wherein said piping is upstream of said at least one        self-cleaning apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1A is a schematic diagram using six retractable knife valves in oneembodiment of the invention.

FIG. 1B is a schematic diagram using six retractable knife valves in oneembodiment of the invention.

FIG. 2 is a schematic diagram using ten retractable valves in oneembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

As employed above and throughout the disclosure, the following terms,unless otherwise indicated, shall be understood to have the followingmeanings.

As used herein, the singular forms “a,” “an,” and “the” include theplural reference unless the context clearly indicates otherwise.

While the present invention is capable of being embodied in variousforms, the description below of several embodiments is made with theunderstanding that the present disclosure is to be considered as anexemplification of the invention, and is not intended to limit theinvention to the specific embodiments illustrated. Headings are providedfor convenience only and are not to be construed to limit the inventionin any manner. Embodiments illustrated under any heading may be combinedwith embodiments illustrated under any other heading.

The use of numerical values in the various quantitative values specifiedin this application, unless expressly indicated otherwise, are stated asapproximations as though the minimum and maximum values within thestated ranges were both preceded by the word “about.” In this manner,slight variations from a stated value can be used to achievesubstantially the same results as the stated value. Also, the disclosureof ranges is intended as a continuous range including every valuebetween the minimum and maximum values recited as well as any rangesthat can be formed by such values. Also disclosed herein are any and allratios (and ranges of any such ratios) that can be formed by dividing arecited numeric value into any other recited numeric value. Accordingly,the skilled person will appreciate that many such ratios, ranges, andranges of ratios can be unambiguously derived from the numerical valuespresented herein and in all instances such ratios, ranges, and ranges ofratios represent various embodiments of the present invention.

A supercritical fluid is a fluid at a temperature above its criticaltemperature and at a pressure above its critical pressure. Asupercritical fluid exists at or above its “critical point,” the pointof highest temperature and pressure at which the liquid and vapor (gas)phases can exist in equilibrium with one another. Above criticalpressure and critical temperature, the distinction between liquid andgas phases disappears. A supercritical fluid possesses approximately thepenetration properties of a gas simultaneously with the solventproperties of a liquid. Accordingly, supercritical fluid extraction hasthe benefit of high penetrability and good solvation.

Reported critical temperatures and pressures include: for pure water, acritical temperature of about 374.2° C., and a critical pressure ofabout 221 bar; for carbon dioxide, a critical temperature of about 31°C. and a critical pressure of about 72.9 atmospheres (about 1072 psig).Near-critical water has a temperature at or above about 300° C. andbelow the critical temperature of water (374.2° C.), and a pressure highenough to ensure that all fluid is in the liquid phase. Sub-criticalwater has a temperature of less than about 300° C. and a pressure highenough to ensure that all fluid is in the liquid phase. Sub-criticalwater temperature may be greater than about 250° C. and less than about300° C., and in many instances sub-critical water has a temperaturebetween about 250° C. and about 280° C. The term “hot compressed water”is used interchangeably herein for water that is at or above itscritical state, or defined herein as near-critical or sub-critical, orany other temperature above about 50° C. (preferably, at least about100° C.) but less than subcritical and at pressures such that water isin a liquid state

As used herein, a fluid which is “supercritical” (e.g. supercriticalwater, supercritical CO₂, etc.) indicates a fluid which would besupercritical if present in pure form under a given set of temperatureand pressure conditions. For example, “supercritical water” indicateswater present at a temperature of at least about 374.2° C. and apressure of at least about 221 bar, whether the water is pure water, orpresent as a mixture (e.g. water and ethanol, water and CO₂, etc). Thus,for example, “a mixture of sub-critical water and supercritical carbondioxide” indicates a mixture of water and carbon dioxide at atemperature and pressure above that of the critical point for carbondioxide but below the critical point for water, regardless of whetherthe supercritical phase contains water and regardless of whether thewater phase contains any carbon dioxide. For example, a mixture ofsub-critical water and supercritical CO₂ may have a temperature of about250° C. to about 280° C. and a pressure of at least about 225 bar.

As used herein, “continuous” indicates a process which is uninterruptedfor its duration, or interrupted, paused or suspended only momentarilyrelative to the duration of the process. Treatment of biomass is“continuous” when biomass is fed into the apparatus without interruptionor without a substantial interruption, or processing of said biomass isnot done in a batch process.

As used herein, “lignocellulosic biomass or a component part thereof”refers to plant biomass containing cellulose, hemicellulose, and ligninfrom a variety of sources, including, without limitation (1)agricultural residues (including corn stover and sugarcane bagasse), (2)dedicated energy crops, (3) wood residues (including sawmill and papermill discards), and (4) municipal waste, and their constituent partsincluding without limitation, lignocellulose biomass itself, lignin, C₆saccharides (including cellulose, cellobiose, C₆ oligosaccharides, C₆monosaccharides, and C₅ saccharides (including hemicellulose, C₅oligosaccharides, and C₅ monosaccharides).

As used herein, “passageway” refers to a hollow chamber of any generalcross-section, including varying cross-sections, used for conveying amaterial.

As used herein with reference to a valve, “open” means that the valvepermits at least partial flow through the passageway. As used hereinwith reference to a valve, “closed” means that the valve permits no flowthrough the passageway. As used herein with reference to a “open” or“closed” valve, “partial” or “partially” means that the valve is not inits fully open or fully closed position, respectively, and thereforepermits at least some flow through the passageway. “Partially open” and“partially closed” may be used interchangeably.

As used herein, “fouling fluid” refers to fluid, including a viscousliquid under the pressure and/or temperature conditions and solid-liquidslurries, that stick to the surfaces of the equipment in which it is incontact causing fouling of small passageways and orifices.

As used herein, “tortuous” refers to a path having more than one twists,bends, or turns.

As discussed above, backpressure control is critical to maintainingprocess conditions. However, with solid-liquid slurries, clogging ofvalves and orifices is a challenge. In addition, back pressure controlvalves cannot respond quickly enough and completely reseal to avoidbleed-through. Process pressure variations must be minimized to maintainprocess control. In the hydraulics of a system, a pump adds mechanicalenergy to the fluid to increase its pressure. The friction of the fluidalong the pipes, valves, reactors and other components creates apressure drop. Some friction losses are fixed, for example through aconstant diameter pipe. Some pressure losses vary, for example through avalve whose opening is varied (large valve opening=less pressure loss).So pressure drop may be controlled by opening or closing the valve. Atortuous piping path is simply a way to increase the pressure drop in ashorter length. By making the piping path tortuous (many turns, twists,etc.), the pressure drop is greater The pressure drop can be designed ina piping system, but once they are installed, the pressure drop is fixed(since the pipes do not move). A partial blockage in the system willalso create a pressure drop, that may be temporary if the partialblockage is eliminated. Thus, controlling the friction of the system ishow the apparatus and methods of the invention compensate for sudden ortemporary pressure changes due to the slurry blocking and hanging upsomewhere along the system. If the fluid were water, the pressure lossesin the system would be very stable, and a control valve at the backwould probably be set in one position and never be touched. In the caseof slurries, the pressure losses in the system fluctuate because ofvariations in consistency of the slurry (clumps), variations inviscosity, variations in temperature, and the like. What is needed is anapparatus and methods that permit constant adjustment of the positionsof the valves to optimize the pressure drop across them. Retractablevalves, especially those arranged in an alternating fashion which createin a tortuous path for the flow of material, that are partially open (orpartially closed) create pressure drops. The retractable valves may becompletely opened, thereby cleaning the valve and valve orifices andpreventing a build up of solids in the passageway, especially whenprocessing viscous fluids and slurries. The apparatus and methods of theinvention, therefore, utilize retractable valves to overcome the issuesassociated with backpressure control by forming a valve array to providethe back pressure control.

Accordingly, in one embodiment, the invention is directed toself-cleaning apparatus for processing of a fouling fluid underpressure, comprising:

-   -   a passageway having at least two stages;    -   a retractable valve positioned in each of said at least two        stages; and

an optional shutoff valve positioned in said passageway;

-   -   wherein said retractable valves form a tortuous path in said        passageway when said retractable valves are partially closed to        permit a pressure drop between said stages; and    -   wherein at least one of said retractable valves is capable of        being in an open position when the other of said retractable        valves are partially closed.        The retractable valves that are used only when the primary        retractable valves forming the tortuous path for the flow of        material are opened for cleaning are referred to alternatively        as “redundant” retractable valves. It is contemplated that        certain retractable valves may be dedicated for use only when        the other retractable valves are open for cleaning. It is also        contemplated, however, that all of the retractable valves may at        one time or another be considered a redundant valve. The        apparatus of the invention may be used advantageously for        processing/transporting solid-liquid slurry after fractionation        of biomass and/or cellulose hydrolysis.

On embodiment of the self-cleaning apparatus is schematically shown inFIG. 1A, using six retractable knife valves 1 a, 1 b, 1 c, 1 d, 1 e, andif in six stages (4 a, 4 b, 4 c, 4 d, 4 e, and 4 f, respectively) inpassageway 2. In this figure, four of the retractable knife valves 1 a,1 b, 1 c, and 1 d, are in a partially open position creating a tortuouspath for the flow of material and two of the retractable knife valves 1e and 1 f are in a fully open position. In FIG. 1B, knife valves 1 c and1 d are opened fully in order to clean them, while knife valves 1 e and1 f are partially closed to take over the duties of the former two. Ineffect, four of the retractable knife valves 1 a, 1 b, 1 e, and 1 f, arein a now partially open position creating a tortuous path for the flowof material and two other of the retractable knife valves 1 c, and 1 dare in a fully open position. A separate shutoff valve, here shown as acone valve 3, may be present for full shut-off.

FIG. 2 is a schematic diagram using ten retractable valves in oneembodiment of the invention. Stages 1 to 8 (5 a, 5 b, 5 c, 5 d, 5 e, 5f, 5 g, and 5 h, where Stage 1 corresponds to 5 a and Stage 8corresponds to 5 h) create the initial pressure letdown and Stages A andB (6 a and 6 b, respectively) allow in-line cleaning for a total of tenstages with ten retractable valves. Flow of materials begins in Stage 1and ends after Stage B. Stages A and B are redundant valves that permitfor opening and cleaning of any two valves in the system (includingStages A and B) while the remaining valves are partially closed.

In another embodiment, the invention is directed to methods for reducingfouling in processing of lignocellulolosic biomass, comprising:

-   -   providing a fouling fluid under pressure in an apparatus        comprising:        -   a passageway having at least two stages;        -   a retractable valve positioned in each of said at least two            stages; and        -   an optional shutoff valve positioned in said passageway;        -   wherein said retractable valves form a tortuous path in said            passageway when said retractable valves are partially closed            to permit a pressure drop between said stages;    -   retracting at least one of said retractable valves to an open        position to form an open retractable valve when the other of        said retractable valves are partially closed to clean said open        retractable valve and to control pressure in said apparatus.

In yet another embodiment, the invention is directed to methods forcontrolling backpressure in processing of lignocellulolosic biomass,comprising:

-   -   providing a fouling fluid under pressure in an apparatus        comprising:        -   a passageway having at least two stages;        -   a retractable valve positioned in each of said at least two            stages; and        -   an optional shutoff valve positioned in said passageway;        -   wherein said retractable valves form a tortuous path in said            passageway when said retractable valves are partially closed            to permit a pressure drop between said stages; and    -   retracting at least one of said retractable valves to an open        position to form an open retractable valve when the other of        said retractable valves are partially closed to clean said open        retractable valve and to control pressure in said apparatus.

In further embodiments, the invention is directed to systems forprocessing viscous fluids, comprising:

-   -   at least one self-cleaning apparatus described herein; and    -   tortuous path piping;    -   wherein said piping is upstream of said at least one        self-cleaning apparatus.

In certain embodiments, the retractable valves are selected from thegroup consisting of a knife valve, needle valve, cone valve, ball valve,lobe valve, and combinations thereof.

The number of retractable valves is dependent on the viscosity of thematerial being processed, velocity, pressure, passageway diameter,fouling characteristics of the material, and the like. In certainembodiments, three retractable valves to about ten retractable valvesare present. In certain preferred embodiments, six retractable valvesare present. In certain preferred embodiments, eight retractable valvesare present. As one skilled in the art will appreciate, the number ofretractable valves will be dependent upon the particular equipmentavailable.

In certain embodiments, at least one of said retractable valves iscapable of being in an open position when the other of said retractablevalves is partially closed.

It is contemplated that the retractable valves (of which there at leasttwo but possibly many additional retractable valves) would open andclose simultaneously and continuously (so that the equipment would neverneed to take any off-line to clean individual valves but would beconstantly cleaning and maintaining adequate pressure.

The array of retractable valves may be in a large number of differentarrangements (i.e., adjacent retractable valves are oriented at about 0°to about 180° to each other and may differ along the array). In certainembodiments, the array of retractable valves forms a tortuous path forthe flow of materials through the passageway. Preferably, adjacentretractable valves are oriented at about 180° to each other to maximizethe pressure loss per valve and minimize the number of total valves.

In certain embodiments, the step of processing includes transportingsaid fouling fluid under pressure.

In certain embodiments, the fouling fluid has a viscosity of at leastabout 10,000 cP. In certain embodiments, the fouling fluid has aviscosity of at least about 15,000 cP.

In certain embodiments, the fouling fluid is a fractionatedlignocellulosic slurry comprising:

-   -   a solid fraction comprising:        -   lignin; and        -   cellulose; and    -   a liquid fraction comprising:        -   soluble C₅ saccharides; and        -   water.

In certain embodiments, the fouling fluid is a slurry comprising:

-   -   a solid fraction comprising:        -   lignin; and    -   a liquid fraction comprising:        -   soluble C₆ saccharides; and        -   water.

In certain embodiments, the passageway is substantially cylindrical.However, other shapes and cross-sections are possible.

In certain embodiments, at least one shutoff valve is present and may beused to fully shutoff flow in the passageway. The shutoff valve maypositioned anywhere in the passageway, including within the array ofretractable valves, before the array of retractable valves, or after thearray of retractable valves in the distal end of the passageway (nearestexit of passageway in direction of flow). Preferably, it is positionedin the distal end of the passageway. Suitable shutoff valves include,but are not limited to, cone valves, ball valves, knife valves, needlevalves, or lobe valves, wherein said valves may be used in the fullyclosed position to stop flow within the passageway.

The pressure drop in the apparatus of the invention will depend upon theparticular material that is being processed. In certain embodiments, thepressure drop in said apparatus is about 50 bars to about 250 bars.

The methods of the invention are preferably run continuously, althoughthey may be run as batch or semi-batch processes.

In certain embodiments, the fractionated lignocellulosic biomass slurryis prepared by contacting said lignocellulosic biomass with a firstreaction fluid comprising hot compressed water and, optionally, carbondioxide; wherein said first reaction fluid further comprises acid, whensaid lignocellulosic biomass comprises softwood; and wherein said firstreaction fluid is at a temperature of at least about 100° C. under apressure sufficient to maintain said first reaction fluid in liquidform. The acid may be an inorganic acid or an organic acid, or an acidformed in situ. Inorganic acid include, but are not limited to: sulfuricacid, sulfonic acid, phosphoric acid, phosphonic acid, nitric acid,nitrous acid, hydrochloric acid, hydrofluoric acid, hydrobromic acid,hydroiodic acid. Organic acids include, but are not limited to,aliphatic carboxylic acids (such as acetic acid and formic acid),aromatic carboxylic acids (such as benzoic acid and salicylic acid),dicarboxylic acids (such as oxalic acid, phthalic acid, sebacic acid,and adipic acid), aliphatic fatty acids (such as oleic acid, palmiticacid, and stearic acid), aromatic fatty acids (such as phenylstearicacid), and amino acids. In certain embodiments, the acid is preferablysulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, or acombination thereof. Gaseous compounds that form acid in situ include,but are not limited to, SO₂.

While the preferred forms of the invention have been disclosed, it willbe apparent to those skilled in the art that various changes andmodifications may be made that will achieve some of the advantages ofthe invention without departing from the spirit and scope of theinvention. Therefore, the scope of the invention is to be determinedsolely by the claims to be appended.

When ranges are used herein for physical properties, such as molecularweight, or chemical properties, such as chemical formulae, allcombinations, and subcombinations of ranges specific embodiments thereinare intended to be included.

The disclosures of each patent, patent application, and publicationcited or described in this document are hereby incorporated herein byreference, in their entirety.

Those skilled in the art will appreciate that numerous changes andmodifications can be made to the preferred embodiments of the inventionand that such changes and modifications can be made without departingfrom the spirit of the invention. It is, therefore, intended that theappended claims cover all such equivalent variations as fall within thetrue spirit and scope of the invention.

What is claimed is:
 1. A self-cleaning apparatus for processing of afouling fluid under pressure, comprising: a passageway extendingcontinuously along an axis and having at least two stages; a retractablevalve positioned in each of said at least two stages, said retractablevalves extending into said passageway and positioned in an orientationdifferent from said axis and positioned in at least one of analternating orientation and at an orientation of about 180 degreesrelative to each other; and an optional shutoff valve positioned in saidpassageway; wherein said retractable valves form a tortuous path in saidpassageway when said retractable valves are partially closed to permit apressure drop between said stages; and wherein at least one of saidretractable valves is capable of being in an open position when theother of said retractable valves are partially closed.
 2. Aself-cleaning apparatus of claim 1, wherein said retractable valve is aknife valve, needle valve, cone valve, ball valve, lobe valve, orcombination thereof.
 3. A self-cleaning apparatus of claim 1, whereinsaid shutoff valve is a cone valve, ball valve, knife valve, needlevalve, or lobe valve.
 4. A self-cleaning apparatus of claim 1, whereinthree retractable valves to about ten retractable valves are present. 5.A self-cleaning apparatus of claim 1, wherein adjacent retractablevalves are oriented at about 180° to each other.
 6. A self-cleaningapparatus of claim 1, wherein said processing is transporting saidfouling fluid under pressure.
 7. A self-cleaning apparatus of claim 1,wherein said fouling fluid has a viscosity of at least about 10,000 cP.8. A self-cleaning apparatus of claim 1, wherein said fouling fluid hasa viscosity of at least about 15,000 cP.
 9. A self-cleaning apparatus ofclaim 1, wherein said fouling fluid is a fractionated lignocellulosicslurry comprising: a solid fraction comprising: lignin; and cellulose;and a liquid fraction comprising: soluble C₅ saccharides; and water. 10.A self-cleaning apparatus of claim 1, wherein said fouling fluid is aslurry comprising: a solid fraction comprising: lignin; and a liquidfraction comprising: soluble C₆ saccharides; and water.
 11. Aself-cleaning apparatus of claim 1, wherein said passageway issubstantially cylindrical.
 12. A self-cleaning apparatus of claim 1,wherein said pressure drop in said apparatus is about 50 bars to about250 bars.
 13. A system for processing viscous fluid, comprising: atleast one self-cleaning apparatus of claim 1; and tortuous path piping;wherein said piping is upstream of said at least one self-cleaningapparatus.
 14. A system of claim 13, wherein said viscous fluidcomprises lignocellulosic biomass or a component part thereof.